UPDATE!
A lot of people have been problems lately, and so have I. Try following the following:
Ok, I've been having problems with my own rig lately (black screen, etc). SO, I did the following.

1. Boot with -s, and do the following commands:
CODE
/sbin/mount -uw /
cd /system/library/extensions
rm -r ATI*
rm -r natit.kext*
reboot
2. Reboot with -f -v.
3. Install this: http://www.mediafire.com/?mz1leyhyolh
4. Then install this: http://rapidshare.de/files/47335568/Enable..._cards.pkg.html
5. Go to /system/library/extensions and open ATINDRV.kext. Go into the plugins folder and delete ATY_motmot.kext.
6. Reboot with -f -v.
7. Enjoy.









A lot of stuff has been happening since netkas first got QE/CI/Res Change on the 4850. Now, the 4830, 4850, 4870, 4870x2, and possibly the 4980 work just fine.





4830 INSTRUCTIONS
1. Follow step 1 from the 4850 instructions below.
2. Download and install the following 2 kext files with Kext Helper: http://rapidshare.de/files/46800670/accel.tar.bz2.html & http://rapidshare.de/files/46858272/Natit.kext.tar.bz2.html.
3. Reboot with -f -v.

You'll probably experience screen bouncing issues, but that can easily be fixed with a simple BIOS flash with higher clock speeds.

4850 INSTRUCTIONS
1. Download this to your desktop, and run the installation package. Don't restart just yet: [Rapidshare.de] http://rapidshare.de/files/45661062/7_rade...rivers.pkg.html [Mediafire] http://www.mediafire.com/?mz1leyhyolh [Badongo] http://www.badongo.com/file/13612115 [DepositFiles] http://depositfiles.com/en/files/pxf70804a
2. Download this: http://rapidshare.de/files/46870770/ATY_Motmot.kext.zip.html and install the kext file with Kext Helper.
3. Reboot with -f -v (kextcache/verbose mode).

You should now have QE/CI and resolution change on your 4850. If you get something weird when you reboot, or if you can't change the resolution, looks at the "BUGS" section below.

4870 INSTRUCTIONS
First, follow the 4850 INSTRUCTIONS above. Then, follow these instructions:
1. Download this: http://www.mediafire.com/download.php?z2atjzyjwm5
2. Backup your existing OpenGL.framework
3. Replace it with the new 10.5.7 framework
4. Repair permissions.
5. Reboot with -f -v.

Your 4870 should now have QE/CI.

4870x2 INSTRUCTIONS
(There may need to be more instructions added for the 4870x2.)
1. Download this: http://rapidshare.de/files/46800670/accel.tar.bz2.html
2. Put everything in the /System/Library/Extensions folder.
3. Repair permissions.
4. Reboot with -f -v.

Your 4870x2 may or may not have QE/CI/Res Change. I may have to update these instructions. I don't even remember where I found them.

4890 INSTRUCTIONS
I'm not sure how to get the 4890 working. Some people have reported to get it working, but I don't know how to do that.





BUGS:
1. You may be getting a jumpy/bouncy screen on your 4850 when you move your mouse.
>>FIX FOR NUMBER 1: Download this package (http://rapidshare.de/files/45735243/Natit_no_powerplay_4800_4600.pkg.html) and install it. Reboot, and it should all be fine.

2. You may get a black screen when changing resolutions.
>>FIX FOR NUMBER 2: Download and install this package (http://rapidshare.de/files/45735159/Natit_with_4850_bios_inside.pkg.html). Reboot, and you should be able to change resolutions without any problems.

3. You may get a light blue screen after doing a hard-restart
>>FIX FOR NUMBER 3: Boot with -s, and do the following commands:

It should go into OS X just fine. From here, you can reinstall the drivers, reboot, and all should be fine again.

4. Sometimes, the mouse/everything will freeze in certain programs.
>>FIX FOR NUMBER 4: You probably have QuartzGL enabled. If so, disable it in OSx86Tools. QuartzGL barely does anything anyway .





Credit needs to go to netkas as I haven't done anything in the development of these drivers.

Some of these instructions may be off or out of date, so if someone could help me update this, then send me a PM with any updated instructions/links/details.